1. Field of the Invention
The present invention relates to an axle positioning structure to provide stable positioning and automatic reposition adopted for using on two objects that can rotate relative to each other, and particularly for an electronic device that has a rotary cover.
2. Related Art
Many portable electronic devices such as notebook computers, mobile phones and the like have a host and a display screen. The display screen can be swiveled relative to the host. When not in use, the display screen can be folded over the host to reduce the size and protect the display screen. When in use, the display screen can be swiveled to form an angle with the host for viewing and operation. To generate the relative rotation between the display screen and the host, they must be hinged with an axle. There are many axle positioning techniques disclosed in the prior art. Reference can be found in Taiwan patent publication numbers 508040, 523127, 526962, 530864, 566816, 572574, 586635, M256670, M245281, etc.
When the axle is adopted on notebook computers, the display screen is unfolded to form an angle with the host and maintained at that angle when in use. To do that, some conventional axle positioning structures use a spring or pad to provide a stable positioning force (such as Taiwan patent publication numbers 586635 and M245281); some provide the stable positioning force through the surface structure of the axle (such as Taiwan patent publication numbers 526962, 530864, 566816 and 572574). Whether providing the positioning force through a spring, pad or surface structure, the axle positioning structure is too complex. Fabrication and assembly are difficult and the cost is too high. To resolve the problem of complex structure, Taiwan patent publication No. 508040 discloses an “Axle radial urging structure” that has a friction member including an arched portion corresponding to the outer diameter of the axle and an arch centrum. Through different diameters of the friction member, the arch centrum has an inner diameter smaller than the outer diameter of the axle. Hence the axle is squeezed during rotation, providing a positioning force. The axle also has a milling surface fitting with the arch centrum to form an automatic latching. Taiwan patent publication No. 508040, providing a tapered design to generate the positioning force for squeezing, has a structure simpler than most of the prior arts mentioned above. However, the arch centrum has varying diameters. That may increase difficulties in the production. Moreover, if the fit between the arch centrum and the axle is too loose, the positioning force is too weak and the stable positioning becomes ineffective. On the other hand, if the fit is too tight, the positioning force is too strong, and the rotation becomes difficult or automatic latching could become impossible.
Taiwan patent publication No. M256670 discloses an “Axle structure” that is the continuous-in-part of No. 508040. It has a sleeve formed with the same diameter. The sleeve has a slit and a flat surface on the inner wall. Through the slit and the flat surface, a squeezing force can be provided. And through the flat surface and a corresponding milling surface, automatic folding can be achieved. Taiwan patent publication No. M256670 also discloses a simpler structure. But its design of the same diameter still has difficulties during production. The flat surface has to be formed on the inner wall of the sleeve. As the typical axle used on portable electronic devices is about 5 to 6 mm, to fabricate the flat surface on the inner wall of such a small size is quite difficult.